Fabrication of metal matrix composites based on aluminum alloys by friction stir processing

Abstract

Friction stir processing (FSP) has been applied for local surface hardening of the plates of hot-deformed АК4-1 aluminum alloy (equivalent of the alloy 2618) by the АК12 aluminum alloy (equivalent of the alloy A413.0). A parallelepiped-shape sample of the AK12 alloy was placed in a groove on the AK4-1 alloy plate. The effect of FSP parameters on resultant microstructure and microhardness was investigated. The FSP was conducted by rotational and traveling speeds of machining tool of 1000 rpm and 30 mm/min, respectively, and axial forces of 5 и 10 kN. In the FSP process, monolithic and defect-free joint of two aluminum alloys, i.e., aluminum matrix composite, was formed. The FSP led to fragmentation and partial dissolution of precipitates of Si and intermetallic phases and to synthesis of hardening intermetallic phase(s). An increase in the alloying of the solid solution due to partial dissolution of precipitates and decomposition of the supersaturated solid solution with a synthesis of the strengthening phase(s) occurred with different intensities in the FSP zones due to different thermomechanical effects. These structural changes were most intense in the stir zone. The microhardness measured on the obtained aluminum matrix composites changes nonmonotonically and depends on the structures in FSP zones.